First, let's look at the cheapest deal you can get. On Tesco, it's a one-year, £20-per-month contract that gives you £60 of calls and texts a month. On Orange, you can get a £29.36 per month contract that includes 150 minutes and 250 texts. On O2, it's almost the same as Orange's deal, within a few pennies. Vodafone offers a two-year, £30 deal with 300 minutes and unlimited texts.

Factor in the cost of the iPhone 3G or a top of the line 32GB iPhone 3GS, and here's what you'll end up spending, assuming you stay on the contract for two years without switching to get a cheaper deal as soon as you can.

The most expensive contract you can get will score you 3,000 minutes and 500 texts on Orange and O2, unlimited texts and calls on Tesco, and 3,000 minutes and unlimited texts on Vodafone.

But what if you're neither a mute call-miser nor a deep-pockets textaholic? We took an average number of calls and texts -- 250 minutes and 150 texts -- as recommended by the BillMonitor contract-comparison Web site, and ran the numbers.

We took the contracts that provided at least this amount of bundled minutes and texts, although most of them overshot the goal.

Orange and O2's contracts both cost around £34 a month and get you 600 minutes and 500 texts. Vodafone's deal is also its cheapest bundle, and so is Tesco's.

It's clear that if you're willing to pay more for the phone up front, you'll save over the long term. Although it's not the cheapest, it may be worth going with Vodafone because of the higher number of included calls and texts, bigger 3G network and lower up-front cost. But on pure numbers, Tesco can't be beat.

We hope that helps bring a tiny ray of light into the iPhone pricing darkness. You should also check out our maps of nationwide 3G coverage, although we recommend you check your postcode with the network's coverage checkers on their Web sites for the most accurate results.